This application is not related to any pending applications.
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1. Field of the Invention
This invention relates in general to subsurface pumps and, more particularly, to an improved pump for producing oil-bearing formations, which minimizes spacing between standing and traveling valve assemblies.
2. Description of Prior Art
A conventional oil well includes a cased well bore with one or more strings of tubing extending downwardly through the casing into the oil or other petroleum fluid contained in the subsurface mineral formation to be produced. The casing is perforated at the level of the production zone to permit fluid flow from the formation into the casing, and the lower end of the tubing string is generally open to provide entry for the fluid in the tubing.
There are basically two types of pumps typically associated with the production of oil bearing formations. Such pumps are defined as tubing pumps, rod pumps and each type of pump has its respective advantages and limitations.
With respect to tubing pumps, a tubing pump provides the largest displacement possible in any size of tubing, typically one quarter inch smaller than the nominal tubing inner diameter (I.D.). Where maximum displacement is needed, the tubing pump is the logical choice.
A tubing pump is the strongest pump made. The heavy wall barrel is connected directly to the bottom of the tubing string with a collar, eliminating the need for a seating assembly on the pump to hold the pump in position. Also, the sucker rod string connects directly to the plunger top cage, eliminating the need for the valve rod required in stationary barrel rod pumps. A disadvantage of the tubing pump is the fact that the tubing string must be pulled in order to replace the pump barrel. This increases the pulling unit time at the well.
The tubing pump is a poor installation in gassy fluid. Because of the length of the standing valve assembly and the puller on the plunger (and frequently the increased bore of an extension nipple) there is a large unswept area at the bottom of the stroke, causing a poor compression ratio. This reduces the effectiveness of the pump valving, and causes low pump efficiency in wells where gas enters the pump suction along with the produced fluid. The increased bore of a tubing pump causes increased load on the rod string and pumping unit. It also increases stroke loss due to rod and tubing stretch. As the pump is set deeper, this stroke loss may actually result in a lower net displacement than would be obtained with the smaller plunger of a rod pump. API RP11L calculations should be made on both the tubing pump and the rod pump to determine the optimum selection.
Rod pumps, however, have several distinguishable structures and each structure has its relative, respective advantage and disadvantage. Discussion now proceeds with respect to the relative merits and disadvantages of each rod pump type.
Stationary Barrel Bottom Anchor Pump
The stationary barrel bottom anchor pump is a pump consideration for deep wells. Like the traveling barrel pump, it has the advantage of having the hydrostatic tubing pressure applied to the outside of the barrel without the disadvantage of the column loading on the plunger bowing the pull tube on the downstroke. A stationary barrel bottom anchor pump is normally recommended for wells with low static fluid level, since the production tubing may be run in with only a short perforated nipple or mud anchor below the seating nipple. Thus, if required, the standing valve of the pump may be less than two feet from the bottom of the well.
The stationary barrel bottom anchor pump is superior to the traveling barrel bottom anchor pump for low fluid level wells as the fluid has only to pass the larger standing valve located immediately above the seating nipple in order to be pumped. The top anchor pump shares this advantage.
The stationary barrel bottom anchor pump is excellent for gassy wells when run in conjunction with a good oil-gas separator or gas anchor. The short rise required for the fluid to pass the standing valve and enter the pump minimizes the tendency to foam and thus reduce efficiency.
The stationary barrel bottom anchor pump is hazardous to run pump in a sandy well as sand can settle tightly in the annulus between the pump and the tubing and stick it tightly in the joint. This type of pump also has the disadvantage on intermittent operation that sand or other foreign material can settle past the barrel rod guide and on top of the pump plunger when the well is shut down, with the possibility of sticking the pump when it is put back on production.
Stationary Barrel Top Anchor Pump
The top anchor pump is recommended in sandy wells where a bottom anchor pump may become sanded in and cause a stripping job. The amount of sand that can settle over the seating ring or top cup is limited to a maximum of about three inches as the fluid discharge from the guide cage keeps it washed free above this point. In this respect, this pump type is superior to the stationary barrel bottom anchor pump as if a travel barrel pump is spaced too high, sand can settle around the pull tube right up to the lowest point reached by the pull plug on the downstroke.
The top anchor pump is specifically recommended in low fluid level gassy or foamy wells where it is particularly advantageous to have the standing valve submerged in the fluid being pumped. A gas anchor should run below the shoe on the tubing.
The outside of the pump barrel of a top anchor pump is at suction pressure, consequently it is more subject to burst or part the barrel tube than a bottom anchor pump. Well depth and the possibility of fluid pound should be carefully considered before running a top anchored pump with a thin wall barrel. If the depth of the well is within the depth recommendations, a top anchor pump is a good general purpose installation.
Irrespective of pump type (either rod or tube) certain criteria must be kept in mind to ensure optimum performance. Those considerations are classified under the sub-categories of pump submergence, gas separation and installations where formation sand can be problematic. The energy to fill a pump during the upstroke must be supplied by the well formation. Therefore, it is essential the pump be installed as low in the well bore as possible to maintain minimum back pressure on the formation. The pump intake should be placed below the perforations or as close above them as possible.
Gas through the pump severely reduces pump efficiency. Where gas interference is a problem a properly designed gas separator should be installed as a part of the subsurface pumping assembly. Various styles are available with each having merits for a particular well condition. It is important to keep the back pressure on the gas at the wellhead at a minimum.
A pump will inherently have problems if sand is allowed to enter. Therefore, it is best to utilize some method of sand control to prevent entrance of sand into the well bore. Gravel packs, screens, and chemical bonding agents are frequently used for this purpose.
Traveling Barrel Bottom Anchor Pump
According to the contemporary art, the movement of the traveling barrel in this pump""s structure keeps the fluid in motion and sand washed clear almost down to the seating nipple. This minimizes the possibility of sand settling around the pump and sticking it, causing a xe2x80x9cwetxe2x80x9d pulling job.
The traveling barrel bottom anchor pump is particularly recommended for wells that are pumped intermittently. Since the ball in the top cage will seat when the well is shut down, sand cannot settle inside of the pump. This is important, as it is possible for even a small quantity of sand settling on top of the plunger of a stationary barrel pump to cause the plunger to stick when the well again starts pumping.
In this pump structure, a sucker rod string connects directly to the top cage which in turn connects to the pump barrel. This top cage is greater in diameter and stronger in construction than a plunger top cage, so fluid load on the upstroke is carried by stronger components than in a stationary barrel pump.
Both the standing and traveling valves on a traveling barrel pump have open type cages. Such cages have more fluid passage than blind cages and are less prone to wear from ball action.
Due to equalized pressure on the outside of the barrel, a bottom anchored pump (either traveling or stationary barrel) has greater resistance to bursting than a top anchored pump. In wells that pound fluid, or in wells where top anchored pumps have experienced burst barrels, the traveling barrel pump is a good application.
The traveling barrel pump is at a disadvantage in wells that have a low static fluid level because of the greater pressure drop between the well bore and the pumping chamber. Since the standing valve is located in the plunger top cage on a traveling barrel pump, it is smaller in diameter and therefore uses a smaller ball and seat than would be used in the standing valve blind cage on a stationary barrel pump.
There is a relationship between pump length, well depth and pump bore which must be observed. When the standing valve (in the plunger top cage) is closed, a column load is transmitted by the plunger through the pull tube and seating assembly into the seating nipple. In a deep well, this load will be sufficient to put a bow in a long pull tube, thus setting up a drag between the pull plug and the pull tube.
It is to this pump structure the instant invention addresses its art enhancing valve placement(s) novelty. The instant invention can be conceptually viewed as a combination, upper barrel connector and cage with connection to a rod string indicated above a fishing neck. A ball and seat located in the bottom of the barrel connector positions ball seats of stationary and traveling valve assemblies closer together pumps of the contemporary art.
An extensive modification and testing, it has been shown that the instant invention practice facilitates traveling and stationary valve proximity approximately three inches distant from on another at the lowermost portion of the reciprocating pumps downward stroke. Thus allowing for enhanced efficiency and far less (adverse) potential for gas lock. The minimizing of such adverse potential is attributed to increased compression realized via closer proximity positioning the positioning of the afore noted valves. The unique structure of the instant invention deserves the longevity of a standard, open cage as in open cages of the contemporary art wear out far more frequently than their associated valve connector due to the lack of material in the walls after machining.
The invention further provides a product that will have a fishing neck in the event that the rod pin should break. Absent the teachings of the instant invention, when a standard, open top cage breaks the only way to retrieve the pump is by pulling the pump tubing.
Various arrangements of pumps have been suggested in the prior art to overcome problems associated with sucker rod pumps for oil wells. U.S. Pat. No. 5,141,416 to Cognevich et al describes a method of manufacturing a plunger for a downhole reciprocating oil well pump. A cylindrical material plunger has its outer surface machined and then is prepared by grit-blasting to receive a coating of ceramic and then the ceramic outer surface is ground to the proper plunger design diameter. Cognevich et al is providing a surface that is longer wearing than the original material surface of the plunger.
U.S. Pat. No. 5,009,000 to Wilmeth et al describes a method of hardening the plunger by forming a boronized case on the plunger. The plunger additionally includes circumferential grooves which tend to trap abrasive particles and help equalize hydrostatic pressure around the plunger.
U.S. Pat. No. 4,968,226 to Brewer describes a plurality of openings formed in the midportion of the pump barrel. These openings allow fluid from the tubing string to enter the intake chamber of the barrel during a portion of the upstroke permitting equilibration of the pressure differential therebetween. Further Brewer provides a traveling valve with a substantially reduced outside diameter which permits fluid around the outside diameter traveling valve cage which permits fluid around its outer surface between the pump barrel and the traveling valve cage. A plunger, sized for substantially fluid tight reciprocation relative to the barrel, is received in the barrel. The plunger has a top with an opening therein and a bottom with an opening therein, and a body. The body defines a cavity continuous with the openings in the top and bottom of the plunger. The length of the plunger is substantially less then the length of the barrel. The plunger has an end portion which, with a portion of the barrel cavity, defines a fluid intake chamber. The volume of the fluid intake chamber therefore varies with reciprocal movement of the plunger and the barrel. A valve associated with the plunger is included for permitting fluid to flow through the plunger only in an upward direction. The openings in the midportion of the barrel cooperate with the relative lengths of the barrel and the plunger to prevent fluid communication between the conduit and the fluid intake chamber during a first phase of the extension stroke and to permit communication between the conduit and the fluid intake chamber during a second phase of the extension stroke.
U.S. Pat. No. 4,662,831 to Bennett discloses a pump for lifting liquids from a well in an earth formation and concurrently fracturing the earth formation. This is accomplished using a pump of the reciprocating piston variety and providing a first valve that permits a quantity of the liquid to be gathered on the downstroke of the pump and lifted during the upstroke of the pump and a second valve that permits a portion of the formation liquids to be forced back in to the earth formation during a first portion of the downstroke of the pump and that prevents further passage of fluids back in to the formation during a second portion of the downstroke of the pump. Also, a third valve for venting formation gases from the interior of the pump near the top of the pump upstroke in order to prevent cushioning of the force of the pump downstroke due to the compressibility of such gases.
U.S. Pat. No. 3,697,199 to Spears discloses a slave valve pump. The pump employs a first piston which is directly moved by an external power source and a slave piston which is moved by the resulting pressure differentials created by the movement of the first piston. The first or lower piston is fixed to the lower end of a cylindrical rod and the upper piston has a tubular form and is adapted to slide over the rod. The axial movement of the upper piston is controlled by the resulting pressure differential crested across its length. The pressure differential acts to move the upper piston to appropriately open or close the outlet ports of the pump which in turn permits fluid to be expelled through the outlet ports and prevents return flow into the pump. On the downstroke of the lower piston, a reduced pressure is created between the slave piston and the lower piston which permits fluid flow into this low pressure area between the two pistons which the lower piston moves past inlet ports and fluid is forced through the inlet ports to the low pressure area.
U.S. Patent No. 5,593,289 relates to an improvement in plunger valve assemblies for reciprocating sucker rod operated subsurface pumps and specifically as to the traveling valves and standing valves. The traveling valve includes a valve body having an inwardly-directed lip at the bottom with the valve seat, ball and cage inserted from the top of the valve body. Further the standing valve has a closed cage formed in the upper portion thereof which is threaded into the bottom of the pump barrel, thus placing the closed cage of the standing valve and the traveling valve in closer proximity at the bottom of the downstroke than prior such pumps.
Though purporting to disclose similar benefits to those offered by the instant invention, the ""289 patent is limited to those pumping structures which rely upon a stationary (non-moving) barrel.
The instant invention addresses itself to the traveling barrel structures of reciprocating pumps and, indeed, incorporates itself therein. The teachings of the ""289 patent which are clearly distinguishable from the instant invention as they rely upon redesigning the barrel cage of a stationary valve body, as well as the plunger cage for traveling barrel body in a manner to reduce the space between the valve and the traveling valve when the pump is at the end of the downstroke. The singular, independent claim of the ""289 patent and its disclosure teach away from the benefits of the moving barrel pump assembly afforded by the instant invention.
Consequently, it is a object of the instant invention to provide a pumping structure which minimizes spacing between traveling and stationary valve assemblies to avoid or minimize potential of gas lock during pumping operations.
The invention provides an improved reciprocating pump for production of fluids from oil and gas wells. The improvement lies in redesigning a traveling barrel cage or traveling valve body in a manner to reduce the space between a stationary valve located generally toward the bottom of a pumping string and the traveling valve such that when the pump is at the end of the downstroke traveling and stationary valves are in closer proximity than can be afforded via pumping technology of the contemporary art.
In view of the limitations and disadvantages of the afore cited prior art, it is apparent that what is needed is a subsurface rod pump with a traveling barrel assembly which effectuates closer proximity valve traveling and stationary valve positions in an effort to reduce or eliminate gas locking during pumping operations. A need unrecognized or ignored by the contemporary art and exceeded by the instant invention.